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Study On Pulse Dynamics In Mode-locked Fiber Lasers With Large Pulse Energy Or High Repetition Rate

Posted on:2018-06-23Degree:DoctorType:Dissertation
Country:ChinaCandidate:W LinFull Text:PDF
GTID:1318330566454692Subject:Materials science
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With regard to the mode-locked fiber lasers,enhancing pulse energies and improving fundamental repetition rates are always highlighted.To develop cavity configurations those are capable of directly achieving pulses with high energies,we have to tackle with the problems of pulse splitting caused by the area theorem?with respect to the conventional or dissipative soliton?.Dissipative soliton resonance,theoretically proposed to evolve without wave-breaking,has been experimentally realized with energy scaling up to?J level.However,considering the complexity of the mode-locked fiber lasers,the occurrence of dissipative soliton can hardly be predicted owing to the lack of a unified theoretical framework.In addition,whether there are critical ingredients that destabilize or distort the dissipative soliton resonance in the practical operation is remained to be explored.In the past few years,the demands on the optical frequency combs with high repetition rate have been dramatically increased,which result in special attention on the relevant laser sources.Among several schemes of acquiring pulse output with high repetition rate,it is beneficial to utilized fiber lasers due to their compact structure and excellent thermal management.Whereas when the repetition rate reaches GHz,the implement of mode-locking in fiber lasers becomes difficult because of the insufficient gain of the fiber.We start from the physical model of the mode-locked fiber lasers and the corresponding numerical results,thus the detailed theory of dissipative soliton resonance or continuous wave mode-locking with high repetition rate is studied.Guided by the theoretical predictions,the cavity parameters are selected and optimized to realized laser pulse with large energy or high repetition rate.The results are depicted as follows:?1?Based on the Podivlov solution and Akhmediev solution of the complex cubic quintic Ginzburg-Landau equation,a composite analytical approach is proposed;as its complement,dissipative soliton solutions of the ninth-order Ginzburg-Landau equation are discussed.According to the technique,soliton dynamics is classified into conventional dissipative soliton,transition state and dissipative soliton resonance.In a mode-locked fiber laser operating at 1.5?m conventional dissipative soliton and transition state are experimentally obtained,and their energies corresponds to 0.374 and 2 nJ,respectively.Additionally,the experimental results well confirm the practicability of the analytical approach.A dissipative soliton resonance with 36 nJ pulse energy is realized at 1.0?m,and further boost in pump power leads to a abnormal evolution of the pulse.?2?Modulational instability of the dissipative soliton resonance is experimentally discovered,it can behave quite different with respect to the optical spectrum,autocorrelation trace and coherence.One has little influence on the primary pulse while the other severely perturbs the background and deteriorates the coherence of dissipative soliton resonance.By analyzing the transfer function in the iterative relation derived by averaging the vectorial model of the fiber laser,the notion of nonlinear phase shock is given.The nonlinear phase shock,acted as the periodic force,is responsible for the appearance of parametric instability.It is revealed by the numerical simulation that the dissipative soliton resonance with parametric instability can evolve to a more homogeneous status with increasing pump power in analogy to the structure relaxation.This exotic phenomenon is experimentally verified by a mode-locked fiber laser at 1.5?m.A spectral-doublet square pulse achieved by experiment is further investigated,which a modulated structure rides above the autocorrelation background.Refer to the real-time measurements by the dispersive Fourier transformation and averaged autocorrelation results,we identify the pulse as a bunch of bright?dark?structures superimposed upon the unstable dissipative soliton resonance.?3?We investigate the mechanisms of the instabilities resulted from a SESAM-based short linear resonator from the theoretical viewpoint,and subsequently yield the parameter range for the continuous wave mode-locking.By adopting a normally dispersive Er3+-doped silica fiber,dissipative soliton with 708 MHz repetition rate is generated in a SESAM-based linear cavity.Thanks to the high gain coefficience of Er3+/Yb3+co-doped phosphate fiber,2.32 GHz,fundamentally mode-locked,1.5?m fiber laser is realized.
Keywords/Search Tags:Fiber laser, dissipative soliton resonance, high repetition rate, modulational instability, Ginzburg-Landau equation
PDF Full Text Request
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